CO2 Concentration Field Research Articles

Zonal demand-controlled ventilation strategy to minimize infection probability and energy consumption: A coordinated control based on occupant detection

Due to the outbreak of COVID-19, an increased risk of airborne transmission has been experienced in buildings, particularly in confined public places. The need for ventilation as a means of infection prevention has become more pronounced given that some basic precautions (like wearing masks) are no longer mandatory. However, ventilating the space as a whole (e.g., using a unified ventilation rate) may lead to situations where there is either insufficient or excessive ventilation in localized areas, potentially resulting in localized virus accumulation or large energy consumption. It is of urgent need to investigate real-time control of ventilation systems based on local demands of the occupants to strike a balance between infection risk and energy saving. In this work, a zonal demand-controlled ventilation (ZDCV) strategy was proposed to optimize the ventilation rates in sub-zones. A camera-based occupant detection method was developed to detect occupants (with eight possible locations in sub-zones denoted as ‘A’ to ‘H’). Linear ventilation model (LVM), dimension reduction, and artificial neural network (ANN) were integrated for rapid prediction of pollutant concentrations in sub-zones with the identified occupants and ventilation rates as inputs. Coordinated ventilation effects between sub-zones were optimized to improve infection prevention and energy savings. Results showed that rapid prediction models achieved an average prediction error of 6 ppm for CO2 concentration fields compared with the simulation under different occupant scenarios (i.e., occupant locations at ABH, ABCFH, and ABCDEFH). ZDCV largely reduced the infection risk to 2.8% while improved energy-saving efficiency by 34% compared with the system using constant ventilation rate. This work can contribute to the development of building environmental control systems in terms of pollutant removal, infection prevention, and energy sustainability.

Optimization of HIsmelt reactor parameters for efficient combustion and heat transfer by numerical simulation

HIsmelt, as one of the non-blast furnace ironmaking processes, is rapidly becoming a focus of attention in the steel industry due to its outstanding advantages in terms of low requirements for raw materials and short and environmentally friendly process. In HIsmelt, a reasonable inner shape of a smelting reduction vessel has an important influence on combustion and heat transfer through changing flow field. Therefore, in this study, the effects of HIsmelt reactor parameters including oxygen-lance insert depth, and smelting reduction vessel body height and throat angle on combustion and heat transfer are investigated through the numerical simulation of the flow field, temperature field, and CO2 concentration field inside smelting reduction vessel. The results show that the heat transfer effect is further improved when increasing the oxygen-lance insert depth because the U-shaped vortex affects a wider area. In addition, as the smelting reduction vessel body height increases and the throat angle decreases, the U-shaped vortex gradually moves away from the melt pool and increases the scouring of the sidewalls. The increased temperature difference and low CO2 concentration indicate that this change reduces the combustion and heat transfer efficiency.

Influence of pore-crack environment on heat propagation of underground coalfield fire: A case study in Daquanhu, Xinjiang, China

The development of pores and cracks in coalfield fire area promote the abnormal temperature, the greenhouse effect, and the release of toxic gases. It is of great significance to study the dynamic distribution characteristics of temperature field and concentration field of typical gas products in a coalfield fire area under different pore-crack environments for revealing the spreading law of underground coalfield fire. In this paper, the combined effect of coal combustion chemical reaction, heat energy transmission, flue gas seepage and pore-crack environment were considered. Taking Daquanhu coalfield fire area as an example, an optimized multi-field coupling model, which included the chemical reaction of coal combustion, convection heat transfer in cracks, heat transfer in porous media, gas seepage and improved partial differential equation of pore-crack evolution was constructed. The coalfield fires area was divided into combustion zone, caving zone, sagging subsidence zone, crack zone. The evolution law of temperature field, CO2 concentration field in the coalfield fire area under different air leakage and geological crack conditions was analysed. The results showed that the temperature development of coalfield fire is divided into rapid heating stage and stable development stage. At the rapid heating stage, the greater the air leakage flow was, the faster the maximum temperature rise in the combustion zone. At the stable development stage, with the air leakage decreased, the thermal buoyancy increased. The greater the number of cracks was, the greater the area of the drying zone (673.15 K < T < 1073.15 K) closed to the crack zone. The influence of crack environment on heat flux in the sagging subsidence zone and crack zone was obvious. The total heat flow in the crack zone was about 25 times that in the caving zone. The relationship between the maximum temperature in the combustion zone and the CO2 concentration at the crack outlet showed an exponential model (ExpGro1 exponential model). The area spread by coalfield fire increased linearly with the rang of surface temperature abnormal. The research results provided a basis for judging the spread trend of coalfield fire and extracting coalfield fire of heat energy.

Evaluation of Simulated CO2 Point Source Plumes from High-Resolution Atmospheric Transport Model

Coal-fired power plants, as major anthropogenic CO2 emission sources, constitute one of the largest contributors to global greenhouse gas emissions. Accurately calculating the dispersion process of CO2 emissions from these point sources is crucial, as it will aid in quantifying CO2 emissions using remote sensing measurements. Employing the Lagrangian Particle Dispersion Theory Model (LPDTM), our study involves modeling CO2 diffusion from point sources. Firstly, we incorporated high-resolution DEM (Digital Elevation Model) and artificial building elements obtained through the Adaptive Deep Learning Location Matching Method, which is involved in CO2 simulation. The accuracy of the results was verified using meteorological stations and aircraft measurements. Additionally, we quantitatively analyzed the influence of terrain and artificial building characteristics on high spatial resolution atmospheric CO2 diffusion simulations, revealing the significance of surface characteristics in dispersion modeling. To validate the accuracy of the LPDTM in high-resolution CO2 diffusion simulation, a comparative experiment was conducted at a power plant in Yangzhou, Jiangsu Province, China. The simulated result was compared with observation from aerial flights, yielding the R2 (Correlation Coefficient) of 0.76, the RMSE (Root Mean Square Error) of 0.267 ppm, and the MAE (Mean Absolute Error) of 0.2315 ppm for the comparison of 73 pixels where the plume intersected with flight trajectories. The findings demonstrate a high level of consistency between the modeled CO2 point source plume morphology and concentration quantification and the actual observed outcomes. This study carried out a quantitative assessment of the influence of surface features on high-resolution atmospheric CO2 point source diffusion simulations, resulting in an enhanced accuracy of the simulated CO2 concentration field. It offers essential technological and theoretical foundations for the accurate quantification of anthropogenic CO2 emissions using top-down approaches.

Simulated long-term evolution of the thermosphere during the Holocene – Part 2: Circulation and solar tides

Abstract. On timescales longer than the solar cycle, long-term changes in CO2 concentration and geomagnetic field have the potential to affect thermospheric dynamics. In this paper, we investigate the thermospheric dynamical response to these two factors during the Holocene, using two sets of ∼12 000-year control runs by the coupled thermosphere–ionosphere model, GCITEM-IGGCAS. The main results indicate that increased/decreased CO2 will enhance/weaken the thermospheric circulation throughout the Holocene, but this effect is non-linear. The cooling effect of CO2 in the thermosphere further provides plausible conditions for atmospheric tidal propagation and increases the thermospheric tidal amplitude. Geomagnetic variations induce hemispheric asymmetrical responses in the thermospheric circulation. Large changes in the circulation occur at high latitudes in the hemisphere with distant magnetic pole drift, inferring a crucial role of geomagnetic non-dipole variations in circulation changes. A positive correlation between the diurnal migrating tide (DW1) and geomagnetic dipole moment is revealed for the first time. The amplitude of DW1 in temperature will increase by ∼1–3 K for each 1×1022 A m2 increase in dipole moment.

Intelligent operation, maintenance, and control system for public building: Towards infection risk mitigation and energy efficiency

During the post-COVID-19 era, it is important but challenging to synchronously mitigate the infection risk and optimize the energy savings in public buildings. While, ineffective control of ventilation and purification systems can result in increased energy consumption and cross-contamination. This paper is to develop intelligent operation, maintenance, and control systems by coupling intelligent ventilation and air purification systems (negative ion generators). Optimal deployment of sensors is determined by Fuzzy C-mean (FCM), based on which CO2 concentration fields are rapidly predicted by combing the artificial neural network (ANN) and self-adaptive low-dimensional linear model (LLM). Negative oxygen ion and particle concentrations are simulated with different numbers of negative ion generators. Optimal ventilation rates and number of negative ion generators are decided. A visualization platform is established to display the effects of ventilation control, epidemic prevention, and pollutant removal. The rapid prediction error of LLM-based ANN for CO2 concentration was below 10% compared with the simulation. Fast decision reduced CO2 concentration below 1000 ppm, infection risk below 1.5%, and energy consumption by 27.4%. The largest removal efficiency was 81% when number of negative ion generators was 10. This work can promote intelligent operation, maintenance, and control systems considering infection prevention and energy sustainability.

Investigation of supercritical CO2 mass transfer in porous media using X-ray micro-computed tomography

Understanding the mass transfer of CO2 into formation brine both qualitatively and quantitatively is important for improving the security of geologic carbon sequestration. In this study, quasi-dynamic X-ray micro-computed tomographic (MCT) imaging was used to track the time-evolution of supercritical CO2 (scCO2) clusters in a sandstone throughout brine injection. A cluster-matching workflow enabled the identification of depletion, merging, and snap-off of the scCO2 clusters, and subsequently the mass transfer coefficient of individual scCO2 clusters was found to range between 3.0×10−5 and 3.5×10−4 mm/s. The macroscopic average mass transfer coefficient was estimated as 1.4×10−4 mm/s. For application to geologic carbon sequestration, these values give an indication of the range of mass transfer coefficients that may be expected for similar state and flow conditions. With the macroscopic average mass transfer coefficient evaluated, we back-calculated the in-situ CO2 concentration field for brine, which provides quantitative insight of the distribution of dissolved CO2 in the sample. Despite slow injection rate (Ca = 10−7), mobilization of small scCO2 clusters was also observed, and was attributed to the combined effect of incomplete dissolution of snapped-off clusters and the reduction in the fluid–fluid interfacial tension (IFT) due to the high local CO2 concentration in brine accompanying scCO2 dissolution. This highlights the coupling of dissolution and mobilization processes and demonstrates the need to understand these interlinked dynamics to improve CO2 storage in geological formations.

Ventilation impacts on infection risk mitigation, improvement of environmental quality and energy efficiency for subway carriages

Subway carriages are enclosed for extended periods of time, with a high density of passengers. Providing a safe, healthy, and comfortable cabin environment is a great challenge, particularly during the COVID-19 pandemic. An increase in ventilation rate can potentially reduce infection probability, which may result in worsening environmental quality (e.g., thermal comfort) and larger energy consumption. Thus, exploring the trade-off among infection risk, environmental quality (with regard to ventilation, thermal comfort, and air quality), and energy consumption is important to optimize ventilation systems for carriages. The effect of different supply air parameters (e.g., velocity and temperature) and ventilation modes of mixing ventilation (MV) & Supply air from the Floor and Return air from the Ceiling (SFRC) was studied. The questionnaires were analyzed to explore passenger dissatisfaction with the carriage environment using a MV system. Simulations were performed to predict the velocity, temperature, and CO2 concentration fields. In addition, the comprehensive benefit was evaluated by analytic hierarchy process (AHP), based on infection probability from the revisited Wells–Riley equation, Air Diffusion Performance Index (ADPI), Predicted Mean Vote (PMV), Pollutant Removal Effectiveness (PRE) and energy consumption estimated by cooling load (Lcool). Compared with MV, the optimized SFRC provided softer draft sensation and decreased CO2 concentration by 42%. The SFRC achieved better comprehensive benefits, with an infection risk reduced to 0.4%, ADPI of 80%, PMV approaching zero, PRE up to 16, and energy efficiency increased by 30%. This work contributes to the optimal design of subway carriage ventilation systems in the post-epidemic era.

U-Net applied to retrieve two-dimensional temperature and CO[formula omitted] concentration fields of laminar diffusion flames

Direct absorption spectroscopy measurement of the 4.3μm CO2 using interband cascade laser with a high spectral resolution, provides theoretical feasibility to retrieve the spatial distribution of CO2 temperature and concentration in flames. However, retrieving temperature and concentrations from the line-of-sight spectral measurements involves solving non-linear and ill-posed problems. Traditional reconstruction algorithms for axisymmetric flames require multiple line-of-sight measurements in both axial and radial directions. The complicated experimental system limits the reconstruction efficiency. Here, a novel reconstruction model is proposed and demonstrated based on the U-Net model, a fully convolutional network model composed by a encoder–decoder path forming a symmetric U-shaped architecture, which only requires measurements of the central axis of the flame to simultaneously and efficiently reconstruct the two-dimensional temperature and CO2 concentration fields for axisymmetric flames. The U-Net model is trained using datasets from simulated temperature, CO2 concentration and their corresponding spectral optical thickness. The proposed U-Net model has been applied to reconstruct the two-dimensional temperature and CO2 concentration fields of two previously measured laminar diffusion flames. Comparing with results from the traditional Abel inversion and two-line atomic fluorescence thermometry methods, the U-Net reconstruction model can better preserve the spatial continuity and correlation of flame temperature and CO2 concentration from information hidden in the flame spectral images, which considerably simplifies the measurement system and improves the reconstruction performance.

Tempo-spatial infection risk assessment of airborne virus via CO2 concentration field monitoring in built environment

The aerosol transmission was academically recognized as a possible transmission route of Coronavirus disease 2019 (COVID-19). We established an approach to assess the indoor tempo-spatial airborne-disease infection risks through aerosol transmission via real-time CO2 field measurement and occupancy monitoring. Compared to former studies, the proposed method can evaluate real-time airborne disease infection risks through aerosol transmission routes. The approach was utilized in a university office. The accumulated infection risk was calculated for three occupants with practical working schedules (from occupancy recording) and one hypothesis occupant with a typical working schedule. COVID-19 was used as an example. Results demonstrated that the individual infection risks diversified with different dwell times and working places in the office. For the three occupants with a practical working schedule, their 3-day accumulated infection risks were respectively 0.050%, 0.035%, 0.027% and 0.041% due to 11.6, 9.0 and 13.8 h exposure with an initial infector percentage of 1%. The results demonstrate that location and dwell time are both important factors influencing the infection risk of certain occupant in built environment, whereas existing literature seldom took these two points into consideration simultaneously. On the contrary, our proposed approach treated the infection risks as place-by-place, time-by-time and person-by-person diversified in the built environment. The risk assessment results can provide early warning for building occupants and contribute to the transmission control of air-borne disease.

Laser-fabricated channeled Cu6Sn5/Sn as electrocatalyst and gas diffusion electrode for efficient CO2 electroreduction to formate

Formate synthesis by CO2 electroreduction reaction (CO2RR) has been considered as a promising strategy for mitigating the excessive CO2. Here, we synthesize Cu6Sn5 alloy on Sn foil (Cu6Sn5/Sn) and gas diffusion electrode (GDE) using laser irradiation. Cu6Sn5/Sn exhibits high formate faradaic efficiency (FEformate) of 87.2% and remains stable at 28.69 mA cm−2 over 14 h. Further, with the help of laser drilling, the channeled Cu6Sn5/Sn used directly as GDE shows increased current density (118 mA cm−2) and steady FEformate (86.69%) in flow cell. Density functional theory (DFT) calculations reveal that the high performance of Cu6Sn5/Sn benefits from the appropriate binding energy of the key intermediates *OCHO. Meanwhile, COMSOL simulation results of CO2 concentration and electric field distribution combined with the results of kelvin probe force microscopy (KPFM) prove that CO2RR prefers to occur around the channels of electrode. More importantly, this laser irradiation method is also available to synthesize other alloy electrocatalysts.

Function Relationship Between Minimum Fresh Air Volume and Personnel Density Meeting the Standard Value of CO2 in Working Area

Reasonable fresh air volume can effectively improve indoor air quality and reduce building energy consumption. In order to achieve the comfortable and energy saving operation of air conditioning and ventilation system, the standard κ-ε turbulence model combined with wall function method is used to simulate and analyze the indoor velocity field, temperature field and CO2 concentration field under different fresh air volume by simulation software. The results show that increasing fresh air volume can improve indoor ventilation efficiency and reduce CO2 concentration; and based on the CO2 concentration, the function between the minimum fresh air volume and the density of indoor personnel is fitted to meet the requirement of comfort and health in indoor working area. The function tion is y = 5.980exp(x/0.343). 3.999.

Influence of viscosity and surface tension on bubble dynamics and mass transfer in a model bubble column

The influence of viscosity and surface tension on bubble dynamics and gas liquid mass transfer has been examined experimentally in a model bubble column using optical measurement methods. Different glycerol-water mixtures, together with the surfactant sodium dodecyl sulphate (SDS), were analysed in this study. Thus the present study covers a viscosity range of 0.86…9.29 mPa⋅s and a surface tension range of 44.8…72.24 mN/m, accordingly, a Morton number range of 1.71 × 10−11…7.04 × 10−7. Shadowgraphy combined with PTV has been used to determine bubble size, velocity, and bubble shrinkage. The liquid velocity and the dissolved CO2 concentration fields have been analysed by particle-image-velocimetry (PIV) and laser-induced fluorescence (LIF), respectively. The bubble sizes and velocities obtained here show a good agreement with correlations proposed in the literature. With decreasing surface tension and decreasing viscosity, the bubble size is decreased but neither the addition of glycerol nor the addition of surfactant was found to be beneficial to mass transfer from the CO2 bubbles into the liquid. Due to the bubble size and velocity change in different mixtures, the liquid flow field is changed as well. The highest velocities could be found in the high viscosity solutions. The liquid velocity profiles are similar for different viscosities, except in the bottom section of the column where the bubble curtain is produced. These results support the existence of a dual effect of viscosity on bubble column fluid dynamics as already stated in the literature before.

Oxy-combustion simulation of ethylene

The paper presents the simulation of the combustion of ethylene intended to be used in hybrid rocket propulsion. The simulation, was performed in ANSYS numerical codes, considering the following assumptions: fuel temperature 700 K and 800 K; pressure in the combustion chamber 1 to 3 bar; overall excess air from 1.5 to 5, in order to determine the case with lowest pollutant species. The simulation displayed the combustion temperature field, the flame OH concentration field, the exhaust gases composition fields, the gases velocity field, NO, CO, CO2 concentration fields and the gases pressure field. The simulation showed the influence of fuel temperature upon the combustion spatial features.

Numerical Study on Air Quality and Thermal Comfort in High Speed Train Compartment with Underfloor Air Supply

In order to improve the air quality and the thermal comfort in the compartment of high speed train, an underfloor air supply mode was presented and compared with the traditional sidewall supply and bottom return mode. The airflow, temperature, CO2 concentration and humidity field were studied by CFD simulation. The Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) were applied as the evaluation criteria. The simulation results showed that the underfloor air supply mode significantly improved the air quality and the thermal comfort. The results provide an effective way to optimize the air distribution and remove the air pollutants in the compartment of high speed train.

Comparing the CarbonTracker and TM5-4DVar data assimilation systems for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; surface flux inversions

Abstract. Data assimilation systems allow for estimating surface fluxes of greenhouse gases from atmospheric concentration measurements. Good knowledge about fluxes is essential to understand how climate change affects ecosystems and to characterize feedback mechanisms. Based on the assimilation of more than 1 year of atmospheric in situ concentration measurements, we compare the performance of two established data assimilation models, CarbonTracker and TM5-4DVar (Transport Model 5 – Four-Dimensional Variational model), for CO2 flux estimation. CarbonTracker uses an ensemble Kalman filter method to optimize fluxes on ecoregions. TM5-4DVar employs a 4-D variational method and optimizes fluxes on a 6° × 4° longitude–latitude grid. Harmonizing the input data allows for analyzing the strengths and weaknesses of the two approaches by direct comparison of the modeled concentrations and the estimated fluxes. We further assess the sensitivity of the two approaches to the density of observations and operational parameters such as the length of the assimilation time window. Our results show that both models provide optimized CO2 concentration fields of similar quality. In Antarctica CarbonTracker underestimates the wintertime CO2 concentrations, since its 5-week assimilation window does not allow for adjusting the distant surface fluxes in response to the detected concentration mismatch. Flux estimates by CarbonTracker and TM5-4DVar are consistent and robust for regions with good observation coverage, regions with low observation coverage reveal significant differences. In South America, the fluxes estimated by TM5-4DVar suffer from limited representativeness of the few observations. For the North American continent, mimicking the historical increase of the measurement network density shows improving agreement between CarbonTracker and TM5-4DVar flux estimates for increasing observation density.

The Influence of Temperature Gradient on the Convective Mixing Phenomena of Geologic Sequestration of CO2

Geological sequestration of CO2 as an effective measure of greenhouse gas emission reduction has seized the attention of many governments and scientists. But few studies concern the effect of temperature field on the CO2 convective mixing process. In fact, the temperature gradient almost exists anywhere in the underground, especially the saline aquifer where the temperature increases with soil depth. A numerical model is developed to simulate the heat and mass transfer in the saline aquifer. The effect of initial temperature field on convective mixing flow is presented in this paper. Boussinesq approximation is used to simplify the governing equations. High accuracy compact difference schemes and Runge-Kutta methods are used to simulate the temperature field and CO2 concentration field. Meanwhile a fourth-order precision iterative algorithm is adopted to solve the pressure Poisson equation. Numerical simulation results show that the effects of temperature field are: accelerating the occurrence of convection, strengthening the convective effect and accelerating the CO2 dissolve.

Stimuli-responsive Pickering emulsions: recent advances and potential applications

Pickering emulsions possess many advantages over traditional surfactant stabilized emulsions. For example, Pickering emulsions impart better stability against coalescence and, in many cases, are biologically compatible and environmentally friendly. These characteristics open the door for their use in a variety of industries spanning petroleum, food, biomedicine, pharmaceuticals, and cosmetics. Depending on the application, rapid, but controlled stabilization and destabilization of an emulsion may be necessary. As a result, Pickering emulsions with stimuli-responsive properties have, in recent years, received a considerable amounts of attention. This paper provides a concise and comprehensive review of Pickering emulsion systems that possess the ability to respond to an array of external triggers, including pH, temperature, CO2 concentration, light intensity, ionic strength, and magnetic field. Potential applications for which stimuli-responsive Pickering emulsion systems would be of particular value, such as emulsion polymerization, enhanced oil recovery, catalyst recovery, and cosmetics, are discussed.

Dissolution of Single Carbon Dioxide Bubbles in a Vertical Pipe

Dissolution of a carbon dioxide (CO2) bubble in the downward flow of water or glycerol-water solutions in a vertical pipe is measured by using an image processing method. Numerical predictions of bubble dissolution using a Sherwood number Sh correlation for a bubble in stagnant water, which was proposed in our previous study, are also carried out to examine its applicability to single bubbles in several fluid property systems. The correlation can predict the bubble dissolution well, during which large bubbles change from Taylor to small bubbles, not only in water but also in glycerol-water solutions. A small bubble in a 50 wt% solution predicted by using the correlation, however, dissolves slightly faster than the experiments in the diameter range of 5–8 mm. CO2 concentration fields visualized by using laser-induced fluorescence show that this is due to the difference in wake structures in the stagnant liquid and in the downward flow, that is, vortex shedding with shape oscillation in the stagnant liquid enhances mass transfer from small bubbles; whereas the closed wake in the downward flow reduces the mass transfer rate. This, in turn, implies that the Sh correlation can give good predictions for long-term bubble dissolution in various stagnant liquids.

Hardware and instrumentation to investigate massive releases of dense phase CO2

CCS (carbon capture and storage) is seen as a possibility to mitigate the global warming effect. The practical implementation of this technique faces a few challenges like safety issues. It is wondered if a massive release affecting the pipeline (may be the most vulnerable part of the CCS chain) would not lead to a disaster remembering what happened in Africa about 28 years ago (about Nyos Lake accident see Eos, 2009). Few experimental observations of large‐scale CO2 releases have been made, and the physics and thermochemistry involved are not fully understood, even if considerable progress has been made theoretically.2 In this paper, the experimental techniques used to investigate this specific problem are described and illustrated with some key results extracted from various projects. Innovative techniques were employed to control the mass flowrate, blowdown, nearfield, and farfield dispersion in the atmosphere. A 2 m3 spherical vessel able to store up to 1000 kg of CO2 at a pressure above 8 MPa was used. Dense CO2 was allowed to spill out via a 50 mm pipe. The temperature, CO2 concentration, and density field of the outside cloud were monitored using thermocouples and concentration probes. Among other results, it was in particular shown that when the mass flowrate is large enough, body forces become significant forcing the cloud to stay on the ground.